Method for transmitting and receiving frame in wireless local area network system and apparatus for the same

ABSTRACT

Disclosed are a method for transmitting and receiving a frame in a wireless local area network (WLAN) system and an apparatus for the same. A method for generating interference/non-interference station lists includes receiving a first frame from a second station, acquiring a receiver address of the first frame from the first frame, and setting, based on whether to receive a second frame that is a response to the first frame from a third station indicated by the receiver address within a preset time from a time when the first frame has been received, the third station as an interference station or a non-interference station. Therefore, the performance of a communication system may be improved.

CLAIM FOR PRIORITY

This application claims priority to Korean Patent Application No.10-2013-0141271 filed on Nov. 20, 2013 and No. 10-2014-0161432 filed onNov. 19, 2014 in the Korean Intellectual Property Office (KIPO), theentire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

Example embodiments of the present invention relate in general totechnology that transmits and receives a frame in a wireless local areanetwork (WLAN) system and more specifically to technology that transmitsand receives a frame in an exposed node state or a blocked node state.

2. Related Art

With the development of information communication technologies, avariety of wireless communication technologies have been developed.Among these technologies, a wireless local area network (WLAN) includestechnology that is used to make wireless connection to the Internetpossible at homes, businesses, or in specific service providing areasusing a portable terminal such as a personal digital assistant (PDA), alaptop computer, a portable multimedia player (PMP), a smart phone, atablet PC, or the like, based on wireless frequency technologies.

A standard for WLAN technology has been developed as the Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard. WLANtechnology according to IEEE 802.11a standard is operated based on anorthogonal frequency division multiplexing (OFDM) method, and mayprovide a transmission speed of up to 54 Mbps at a 5 GHz band. WLANtechnology according to IEEE 802.11b standard is operated based on adirect sequence spread spectrum (DSSS) method and may provide atransmission speed of up to 11 Mbps at a 2.4 GHz band. WLAN technologyaccording to IEEE 802.11g standard is operated based on the OFDM methodor the DSSS method, and may provide a transmission speed of up to 54Mbps at the 2.4 GHz band.

WLAN technology according to IEEE 802.11n standard is operated at the2.4 GHz band and 5 GHz band based on the OFDM method, and may provide,when using a multiple to input multiple output-OFDM (MIMO-OFDM) method,a transmission speed of up to 300 Mbps with respect to four spatialstreams. The WLAN technology according to IEEE 802.11n standard maysupport a channel bandwidth of up to 40 MHz, and in this case, provide atransmission speed of up to 600 Mbps.

As such WLAN technology becomes more prevalent and its applicationsbecome more diverse, there is increasing a demand for new WLANtechnology that can support a higher processing throughput than a dataprocessing speed supported by IEEE 802.11n. Very high throughput (VHT)WLAN technology is one among IEEE 802.11 WLAN technologies proposed tosupport a data processing speed of 1 Gbps or higher. Among these, IEEE802.11ac has been developed as a standard for providing VHT in a band at5 GHz or less, and IEEE 802.11ad has been developed as a standard forproviding VHT in a band at 60 GHz.

In a system based on such WLAN technology, there is a problem that theperformance of the WLAN system is degraded due to an exposed node and ablocked node.

SUMMARY

Accordingly, example embodiments of the present invention are providedto substantially obviate one or more problems due to limitations anddisadvantages of the related art.

Example embodiments of the present invention provide a method fortransmitting and receiving a frame in an exposed node state.

Example embodiments of the present invention also provide a method fortransmitting and receiving a frame in a blocked node state.

In some example embodiments, a method for generatinginterference/non-interference station lists which is performed in afirst station, includes: receiving a first frame from a second station;acquiring a receiver address of the first frame from the first frame;and setting, based on whether to receive a second frame that is aresponse to the first frame from a third station indicated by thereceiver address within a preset time from a time when the first framehas been received, the third station as an interference station or anon-interference station.

Here, the setting may include setting the third station as theinterference station when normally receiving the second frame from thethird station within the preset time.

Also, the setting may include setting the third station as thenon-interference station when failing to normally receive the secondframe from the third station within the preset time.

Also, the method may further include generating theinterference/non-interference station lists including identificationinformation of the third station and reception power information of thesecond frame measured in the first station.

Also, the first frame may be a probe request frame, an authenticationrequest frame, an association request frame, a reassociation requestframe, a request to send (RTS) frame, a data frame, or a blockacknowledgement request (BAR) frame.

Also, the preset time may be a short inter-frame space (SIFS).

In other example embodiments, a method for transmitting a frame which isperformed in a first station, includes: receiving a first frame from asecond station; acquiring a receiver address of the first frame from thefirst frame; and determining whether a third station indicated by thereceiver address is an interference station or a non-interferencestation based on interference/non-interference station lists generatedin advance.

Here, the first frame may be an RTS frame, a data frame, or a BAR frame.

Also, the interference station list of the interference/non-interferencestation lists may include at least one station that transmits a responseto the first frame within a first preset time, and the non-interferencestation list of the interference/non-interference station lists mayinclude at least one station that fails to transmit the response to thefirst frame within the first preset time.

Also, the first preset time may be an SIFS.

Also, the method may further include transmitting a third frame after asecond preset time from a time when the first frame has been receivedwhen the third station is determined as the non-interference station.

Also, the transmitting of the third frame may include acquiringreception power information about a second frame transmitted by thethird station from the interference/non-interference station lists,retrieving a channel based on the reception power information during thesecond preset time, and transmitting the third frame after the secondpreset time when a signal exceeding a preset signal size does not existduring the second preset time.

Also, the second preset time may be a distributed coordination function(DCF) inter-frame space (DIFS), a point coordination function (PCF)inter-frame space (PIFS), or an arbitration inter-frame space (AIFS).

Also, the third frame may be a frame to request stopping frametransmission to the first station.

Also, the third frame may include at least one of a transmitter addressof the third frame, information about a period during which transmissionof the frame is stopped, and a receiver address of the third frame.

In still other example embodiments, a first station includes: aprocessor; and a memory in which at least one program command executedthrough the processor is stored, wherein the at least one programcommand is executable to perform steps of: receiving a first frame froma second station; acquiring a receiver address of the first frame fromthe first frame; and determining a third station indicated by thereceiver address as an interference station or a non-interferencestation based on interference/non-interference station lists generatedin advance.

Here, the interference station list of the interference/non-interferencestation lists may include at least one station that transmits a responseto the first frame within a first preset time, and the non-interferencestation list of the interference/non-interference station lists mayinclude at least one station that fails to transmit the response to thefirst frame within the first preset time.

Also, the at least one program command may be executable to furtherperform a step of transmitting a third frame after a second preset timefrom a time when the first frame has been received, when the thirdstation is determined as the non-interference station.

Also, the transmitting of the third frame may include acquiringreception power information about a second frame transmitted by thethird station from the interference/non -interference station lists,retrieving a channel based on the reception power information during thesecond preset time, and transmitting the third frame after the secondpreset time when a signal exceeding a preset signal size does not existduring the second preset time.

Also, the third frame may be a frame to request stopping frametransmission to the first station.

BRIEF DESCRIPTION OF DRAWINGS

Example embodiments of the present invention will become more apparentby describing in detail example embodiments of the present inventionwith reference to the accompanying drawings, in which:

FIG. 1 is a block diagram illustrating an example of a station thatperforms methods according to an embodiment of the present invention;

FIG. 2 is a conceptual diagram illustrating an example of aconfiguration of a wireless local area network (WLAN) system accordingto the Institute of Electrical and Electronics Engineers (IEEE) 802.11;

FIG. 3 is a flowchart illustrating an association procedure of aterminal in an infrastructure basic service set (BSS);

FIG. 4 is a conceptual diagram illustrating an exposed node problem;

FIG. 5 is a conceptual diagram illustrating a case in which a solutionto an exposed node problem is applied;

FIG. 6 is a conceptual diagram illustrating a case in which othersolution to an exposed node problem is applied;

FIG. 7 is a conceptual diagram illustrating a blocked node problem;

FIG. 8 is a conceptual diagram illustrating effect of a blocked node ona communication system;

FIG. 9 is a block diagram illustrating a configuration of a processorconstituting a station;

FIG. 10 is a flowchart illustrating a method for generatinginterference/non-interference station lists according to an embodimentof the present invention;

FIG. 11 is a flowchart illustrating a method for transmitting a frameaccording to an embodiment of the present invention;

FIG. 12 is a conceptual diagram illustrating an example of a method fortransmitting a data frame according to an embodiment of the presentinvention;

FIG. 13 is a conceptual diagram illustrating an example of a method fortransmitting a prevent to send (PTS) frame according to an embodiment ofthe present invention;

FIG. 14 is a conceptual diagram illustrating another example of a methodfor transmitting a data frame according to an embodiment of the presentinvention;

FIG. 15 is a conceptual diagram illustrating another example of a methodfor transmitting a PTS frame according to an embodiment of the presentinvention;

FIG. 16 is a conceptual diagram illustrating still another example of amethod for transmitting a data frame according to an embodiment of thepresent invention; and

FIG. 17 is a conceptual diagram illustrating still another embodiment ofa method for transmitting a PTS frame according to an embodiment of thepresent invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments of the present invention are disclosed herein.However, specific structural and functional details disclosed herein aremerely representative for purposes of describing example embodiments ofthe present invention, and example embodiments of the present inventionmay be embodied in many alternative forms and should not be construed aslimited to example embodiments of the present invention set forthherein.

Accordingly, while the invention is susceptible to various modificationsand alternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theinvention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention. Like numbers referto like elements throughout the description of the figures.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(i.e., “between” versus “directly between”, “adjacent” versus “directlyadjacent”, etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. In thedrawings and description, elements that appear in more than one drawingand/or elements that are mentioned in more than one place in thedescription are always denoted by the same respective reference numeralsand are not described in detail more than once.

In the entire specification, a station (STA) is an arbitrary functionalmedium including a medium access control (MAC) layer defined by theInstitute of Electrical and Electronics Engineers (IEEE) 802.11standard, and a physical layer interface with respect to a wirelessmedium. STAs may be divided into STAs that are access points (APs) andSTAs that are non-APs. An STA that is an AP may be simply referred to asan AP, and an STA that is a non-AP may be simply referred to as aterminal.

The STA may include a processor and a transceiver, and may furtherinclude a user interface, a display device, and the like. The processordenotes a unit that is designed to generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network, and performs a variety of functions for controllingthe STA. The transceiver may be functionally connected to the processor,and is a unit that is designed to transmit and receive a frame throughthe wireless network for the STA.

The AP may refer to a centralized controller, a base station (BS), aradio access station, a node-B, an evolved node B, a relay, a mobilemultihop relay (MMR)-BS, a base transceiver system (BTS), a sitecontroller, or the like, and may include some or all functions thereof.

The terminal (that is, non-AP) may refer to a wirelesstransmission/reception unit (WTRU), user equipment (UE), a user terminal(UT), an access terminal (AT), a mobile station (MS), a mobile terminal,a subscriber unit, a subscriber station (SS), a wireless device, amobile subscriber unit, or the like, and may include some or allfunctions thereof.

Here, the terminal may refer to a desktop computer, a laptop computer, atablet PC, a wireless phone, a mobile phone, a smart phone, a smartwatch, a smart glass, an e-book reader, a portable multimedia player(PMP), a portable gaming device, a navigation device, a digital camera,a digital multimedia broadcasting (DMB) player, a digital audiorecorder, a digital audio player, a digital picture recorder, a digitalpicture player, a digital video recorder, a digital video player, or thelike.

FIG. 1 is a block diagram illustrating an example of a station thatperforms methods according to an embodiment of the present invention.

Referring to FIG. 1, a station 100 may include at least one processor110, a memory 120, and a network interface device 130 that is connectedto a network to perform communication. In addition, the station 100 mayfurther include an input interface device 140, an output interfacedevice 150, a storage device 160, and the like. The respectivecomponents included in the station 100 may be connected by a bus 170 toperform communication with each other.

The processor 110 may execute program commands stored in the memory 120and/or the storage device 160. The processor 110 may include a centralprocessing unit (CPU), a graphics processing unit (GPU), or a dedicatedprocessor in which methods according to the present invention areperformed. The memory 120 and the storage device 160 may be constitutedof a volatile storage medium and/or non-volatile storage medium. Forexample, the memory 120 may be constituted of a read only memory (ROM)and/or a random access memory (RAM).

Embodiments of the present invention may be applied to a wireless localarea network (WLAN) system according to IEEE 802.11, and also applied toother communication systems as well as the WLAN system according to IEEE802.11.

For example, the embodiments of the present invention may be applied toa portable Internet such as a wireless personal area network (WPAN), awireless body area network (WBAN), a wireless broadband internet(WiBro), or a world interoperability for microwave access (WiMax), a 2Gmobile communication network such as a global system for mobilecommunication (GSM) or a code division multiple access (CDMA), a 3Gmobile communication network such as a wideband code division multipleaccess (WCDMA) or a cdma2000, a 3.5G mobile communication network suchas a high speed downlink packet access (HSDPA) or a high speed uplinkpacket access (HSUPA), a 4G mobile communication network such as a longterm evolution (LTE) or LTE-Advanced, a 5G mobile communication network,and the like.

FIG. 2 is a conceptual diagram illustrating an example of aconfiguration of a WLAN system according to IEEE 802.11.

Referring to FIG. 2, the WLAN system according to IEEE 802.11 mayinclude at least one basic service set (BSS). BSS may include a set ofstations STA1, STA2 (AP1), STA3, STA4, STA5 (AP2), STA6, STA7, and STA8in which synchronization is successfully performed to communicate witheach other, and is not a concept which means a specific region.

The BSSs may be divided into infrastructure BSSs and independent BSSs(IBSSs). Here, BSS1 and BSS2 mean the infrastructure BSSs, and BSS3means the IBSS.

The BSS1 may include a first terminal STA1, a first AP (STA2 (AP1)) thatprovides distribution services, and a distribution system (DS) thatassociates a large number of APs (STA2 (AP1), STA5 (AP2)). In the BSS1,the first AP (STA2 (AP1)) may manage the first terminal STA1.

The BSS2 may include a third terminal STA3, a fourth terminal STA4, asecond AP (STA5 (AP2)) that provides distribution services, and a DSthat associates a large number of APs (STA2 (AP1), STA5 (AP2)). In theBSS2, the second AP (STA5 (AP2)) may manage the third terminal STA3 andthe fourth terminal STA4.

The BSS3 means an IBSS that is operated in an ad-hoc mode. In the BSS3,an AP that is a centralized management entity performing a managementfunction at the center does not exist. That is, the terminals STA6,STA7, and STA8 are managed in a distributed manner in the BSS3. In theBSS3, all of the terminals STA6, STA7, and STA8 may mean a mobileterminal, and association with the DS is not allowed, and therefore aself-contained network is formed.

The APs (STA2 (AP1), STA5 (AP2)) may provide association with the DSthrough a wireless medium for the terminals STA1, STA3, and STA4 coupledto the APs (STA2 (AP1), STA5 (AP2)). In the BSS1 or the BSS2,communication among the terminals STA1, STA3, and STA4 is generallyperformed through the APs (STA2 (AP1), STA5 (AP2)), but in a case inwhich a direct link is set, direct communication among the terminalsSTA1, STA3, and STA4 is possible.

A plurality of infrastructure BSSs may be associated with one anotherthrough the DS. The plurality of BSSs associated with each other throughthe DS are referred to as an extended service set (ESS). Objects STA1,STA2 (AP1), STA3, STA4, and STA5 (AP2) included in the ESS maycommunicate with one another, and arbitrary terminals STA1, STA3, andSTA4 within the same ESS may be moved from one BSS to other BSSs whilecommunicating without interruption.

The DS is a mechanism for a single AP to communicate with other APs, andaccordingly, the AP may transmit a frame for terminals coupled to theBSS managed by the AP itself, or transmit the frame for an arbitraryterminal moved to the other BSSs. In addition, the AP may transmit andreceive the frame with an external network such as a wired network orthe like. Such a DS is not necessarily a network, and the DS is notlimited to its shape as long as it can provide predetermineddistribution services defined in IEEE 802.11. For example, the DS may bea wireless network such as a mesh network, or a physical structure forallowing APs to be associated with one another.

In the infrastructure BSS, the terminal STA may be associated with theAP. The terminal STA may transmit and receive data when being associatedwith the AP.

FIG. 3 is a flowchart illustrating an association procedure of aterminal in an infrastructure BSS.

Referring to FIG. 3, an association procedure of the terminal STA in theinfrastructure BSS may be roughly divided into a probe step that detectsan AP, an authentication step with the detected AP, and an associationstep with the AP having performed an authentication procedure.

The terminal STA may detect neighbor APs using a passive scanning methodor an active scanning method. In a case of using the passive scanningmethod, the terminal STA may detect the neighbor APs by overhearingbeacons transmitted by APs. In a case of using the active scanningmethod, the terminal STA may detect the neighbor APs by transmitting aprobe request frame and receiving a probe response frame that is aresponse to the probe request frame from the APs.

When detecting the neighbor APs, the terminal STA may perform anauthentication step with the detected AP. In this case, the terminal STAmay perform the authentication step with a plurality of APs.Authentication algorithms according to IEEE 802.11 may be divided intoan open system algorithm that exchanges two authentication frames, ashared key algorithm that exchanges four authentication frames, and thelike.

Based on the authentication algorithm according to IEEE 802.11, theterminal STA may complete authentication with the AP by transmitting anauthentication request frame and receiving an authentication responseframe that is a response to the authentication request frame from theAP.

When completing authentication, the terminal STA may perform anassociation step with the AP. In this case, the terminal STA may selectone AP among the APs having performed the authentication step with theterminal STA itself, and perform an association step with the selectedAP. That is, the terminal STA may complete association with the selectedAP by transmitting an association request frame to the selected AP andreceiving an association response frame that is a response to theassociation request frame from the selected AP.

FIG. 4 is a conceptual diagram illustrating an exposed node problem.

Referring to FIG. 4, a first access point (AP) 410 and a first terminal411 may constitute a first infrastructure BSS 401, and a second AP 420and a second terminal 421 may constitute a second infrastructure BSS402. The first AP 410 may receive a frame transmitted from the firstterminal 411, but may not receive frames transmitted from the second AP420 and the second terminal 421.

The first terminal 411 may receive frames transmitted from the first AP410 and the second terminal 421, but may not receive a frame transmittedfrom the second AP 420. The second terminal 421 may receive framestransmitted from the first terminal 411 and the second AP 420, but maynot receive a frame transmitted from the first AP 410. The second AP 420may receive a frame transmitted from the second terminal 421, but maynot receive frames transmitted from the first AP 410 and the firstterminal 411.

Here, in an environment in which two infrastructure BSSs are adjacent toeach other (or overlapped environment), an exposed node problem will bedescribed, but may occur even in an environment in which at least twoAd-hoc networks exist. Hereinafter, in a case in which the firstterminal 411 is associated with the first AP 410 to transmit a frame,effects of the first infrastructure BSS 401 on the second infrastructureBSS 402 will be described.

Each of communication objects (that is, AP or terminal) may retrieve achannel before transmitting a corresponding frame in a carrier sensemultiple access (CSMA) method. Thus, the second terminal 421 maydetermine that the first terminal 411 transmits the corresponding framethrough channel retrieval before transmitting the corresponding frame,and may not transmit the corresponding frame until frame transmission ofthe first terminal 411 is completed.

For example, according to the IEEE 802.11 standard, the second terminal421 may receive a request to send (RTS) frame transmitted from the firstterminal 411 based on a clear channel assessment (CCA) method of an MAClayer. The second terminal 421 may set a network allocation vector (NAV)based on a period indicated by a duration field included in an MACheader of the RTS frame, and may not transmit a corresponding frame fora period during which the NAV is set.

Meanwhile, in a case in which the first AP 410 that receives the frametransmitted from the first terminal 411 is positioned outside aninterference region of the second terminal 421 (that is, a case in whichthe frame transmitted from the second terminal 421 is not normallyreceived from the first AP 410), although the second terminal 421transmits the corresponding frame to the second AP 420 during which thefirst terminal 411 transmits the corresponding frame to the first AP410, the first AP 410 may normally receive the frame transmitted fromthe first terminal 411, and the second AP 420 may also normally receivethe frame transmitted from the second terminal 421.

In this manner, the reason why only one terminal 411 or 421 shouldtransmit the corresponding frame although each of the APs 410 and 420can simultaneously receive the corresponding frame is because aprocedure of retrieving a channel is first performed before transmittingthe corresponding frame in the CSMA method. This is called an exposednode problem.

The exposed node problem corresponds to a case in which a correspondingframe is not transmitted although it can be transmitted, and thereforethe transmission capacity of the communication system may be accordinglyreduced. In a case of the CSMA method that exchanges an RTS frame and aclear to send (CTS) frame, the solution to the exposed node problem hasbeen conceptually known. That is, in a case in which the communicationobject receives the RTS frame but cannot receive the CTS frame that isthe response to the RTS frame, it is possible to transmit thecorresponding frame within a signal range of the communication objectthat has transmitted the RTS frame. However, when this solution isapplied to an actual system, a time to listen cannot be sufficientlyensured due to characteristics of the CSMA method on the assumption of alisten before talk (LBT) method, and therefore the communication objectcannot transmit the corresponding frame simultaneously with othercommunication objects. This problem will be described in detail asbelow.

FIG. 5 is a conceptual diagram illustrating a case in which a solutionto an exposed node problem is applied, and FIG. 6 is a conceptualdiagram illustrating a case in which other solution to an exposed nodeproblem is applied.

Referring to FIGS. 5 and 6, a first station STA1 and a second stationSTA2 may constitute the first infrastructure BSS 401 of FIG. 4. A thirdstation STA3 and a fourth station STA4 may constitute the secondinfrastructure BSS 402 of FIG. 4. Each of the stations STA1, STA2, STA3,and STA 4 may refer to an AP or a terminal.

For example, the first station STA1 may be the same as the firstterminal 411 of FIG. 4, and the second station STA2 may be the same asthe first AP 410 of FIG. 4. The third station STA3 may be the same asthe second terminal 421 of FIG. 4, and the fourth station STA4 may bethe same as the second AP 420 of FIG. 4.

First, the first station STA1 may retrieve a channel during adistributed coordination function (DCF) inter-frame space (DIFS), andwhen a signal exceeding a preset signal size is not detected based onthe retrieval result (that is, when the channel is in an idle state),transmit an RTS frame 501 to the second station STA2 after contentionwindow (CW) according to a random back-off procedure. When normallyreceiving the RTS frame 501, the second station STA2 may transmit a CTSframe 502 as a response to the RTS frame 501 to the first station STA1.In this instance, the second station STA2 may transmit the CTS frame 502after a short inter-frame space (SIFS) from a reception termination timeof the RTS frame 501.

When normally receiving the CTS frame 502, the first station STA1 maytransmit a data frame 503 to the second station STA2 after the SIFS froma reception termination time of the CTS frame 502. When normallyreceiving the data frame 503, the second station STA2 may transmit anacknowledgement (ACK) frame 504 as a response to the data frame 503 tothe first station STA1. In this instance, the second station STA2 maytransmit the ACK frame 504 after the SIFS from a reception terminationtime of the data frame 503. When receiving the ACK frame 504, the firststation STA1 may determine that the data frame 503 is normally receivedfrom the second station STA2.

Meanwhile, when receiving the RTS frame 501 but failing to receive theCTS frame 502 that is the response to the RTS frame 501 (that is, whenit is determined that the third station STA3 is an exposed node), thethird station STA3 may attempt to transmit the corresponding frame aftera reception termination time of the CTS frame 502. In this case, thethird station STA3 may transmit the corresponding frame during theperiod from the reception termination time of the CTS frame 502 to areception start time of the ACK frame 504 (that is, 2×SIFS+transmissionperiod of data frame 503).

That is, the third station STA3 may retrieve a corresponding channelduring the DIFS after the reception termination time of the CTS frame502, and when a signal exceeding a preset signal size is not, detectedbased on the retrieval result (that is, in a case in which the channelis in an idle state), transmit an RTS frame 505 to the fourth stationSTA4 after contention window (CW) according to the random back-offprocedure. However, after the SIFS from the reception termination timeof the CTS frame 502 (generally, SIFS<DIFS), the data frame 503 may betransmitted from the first station STA1, and the third station STA3 maydetect the data frame 503 when retrieving the channel.

The data frame 503 corresponds to a high interference signal from theside of the third station STA3, and therefore it is difficult for thethird station STA3 to acquire a sufficient signal to noise ratio (SNR)with respect to frames transmitted from other communication objects.Thus, it is difficult for third station STA3 to accurately determine achannel state (that is, busy or idle) during the DIFS after thereception termination time of the CTS frame 502. That is, the thirdstation STA3 cannot ensure the DIFS that is a time for determining thechannel state, and thereby may not transmit the frame simultaneouslywith the first station STA1.

If the time for determining the channel state is defined as an SIFSshorter than the DIFS, the third station STA3 may transmit thecorresponding frame simultaneously with the first station STA1. However,to define the time for determining the channel state as the SIFS is togive the same priority as that of the communication object that won thecompetition to the third station STA3, and therefore this does notcorrespond to the CSMA method. Thus, it is not easy that theabove-described solution to the exposed node problem is directly appliedto the communication system according to the CSMA method.

In other embodiment, the third station STA3 may directly transmit a dataframe 509 to the fourth station STA4 without a RTS-CTS protocol. Thatis, when the channel is in an idle state (that is, when the CTS frame502 in response to the RTS frame 501 is not received) during the presettime (XIFS) from a reception termination time of the RST frame 501, thethird station STA3 may transmit the data frame 509 to the fourth stationSTA4 after contention window CW according to the random back-offprocedure. Here, the length of the data frame 509 may be less than thelength corresponding to ‘a transmittable time of the third stationSTA3.’

When the data frame 509 is received, the fourth station STA4 maytransmit an ACK frame 510 in response to the data frame 509 to the thirdstation STA3. In this instance, the fourth station STA4 may transmit theACK frame 510 after a transmission termination time of the data frame503 to avoid collision between the data frame 503 and the ACK frame 510.Alternatively, when it is set that a response about reception success orfailure of the data frame 509 between the third station STA3 and thefourth station STA4 is not transmitted and received, the fourth stationSTA4 may not transmit the ACK frame 510 in response to the data frame509 if the data frame 509 has been received.

Meanwhile, the blocked node problem is a problem that occurs when theexposed node problem is not solved, and therefore the transmissioncapacity of the communication system may be reduced due to the blockednode problem.

FIG. 7 is a conceptual diagram illustrating a blocked node problem.

Referring to FIG. 7, a first AP 610 and a first terminal 611 mayconstitute a first infrastructure BSS 601, and a second AP 620 and asecond terminal 621 may constitute a second infrastructure BSS 602. Thefirst AP 610 may receive a frame transmitted from the first terminal611, but may not receive frames transmitted from the second AP 620 andthe second terminal 621.

The first terminal 611 may receive frames transmitted from the first AP61.0 and the second terminal 621, but may not receive a frametransmitted from the second AP 620. The second terminal 621 may receiveframes transmitted from the first terminal 611 and the second AP 620,but may not receive a frame transmitted from the first AP 610. Thesecond AP 620 may receive a frame transmitted from the second terminal621, but may not receive frames transmitted from the first AP 610 andthe first terminal 611.

Here, in an environment in which two infrastructure BSSs are adjacent toeach other (or overlapped environment), a blocked node problem will bedescribed, but may occur even in an environment in which at least twoAd-hoc networks exist.

The first terminal 611 may transmit an RTS frame to the first AP 610. Inthis case, the second terminal 621 may receive the RTS frame transmittedfrom the first terminal 611, and thereby may set an NAV based on aperiod indicated by a duration field included in an MAC header of theRTS frame, and may not transmit a corresponding frame for a periodduring which the NAV is set. In this instance, frame transmission isstopped by NAV setting, and therefore the second terminal 621 maycorrespond to a blocked node.

Meanwhile, the second AP 620 cannot receive the RTS frame transmittedfrom the first terminal 611, and thereby can transmit the correspondingframe regardless of NAV that is set based on the corresponding RTSframe. That is, while the second terminal 621 is operated in a state inwhich the second terminal 621 cannot transmit the corresponding frame byNAV setting, the second AP 620 may transmit the RTS frame to the secondterminal 621 when there is data to be transmitted to the second terminal621.

In this case, the second terminal 621 may face two cases. In a firstcase, an RTS frame transmitted from the first terminal 611 or a dataframe collides with an RTS frame transmitted from the second AP 620, andtherefore the second terminal 621 cannot normally receive the RTS frametransmitted from the second AP 620. In a second case, when normallyreceiving the RTS frame transmitted from the second AP 620, the secondterminal 621 cannot transmit a CTS frame that is a response to the RTSframe to the second AP 620 by NAV that is set based on the RTS framereceived from the first terminal 611.

In both cases, the second AP 620 cannot receive the CTS frame that isthe response to the RTS frame from the second terminal 621, and therebyre-transmits the RTS frame to the second terminal 621. Thus, the time iswasted by the time during which the RTS frame is re-transmitted to thesecond terminal 621, and this is called the blocked node problem.

FIG. 8 is a conceptual diagram illustrating effect of a blocked node ona communication system.

Referring to FIG. 8, a first station STA1 and a second station STA2 mayconstitute the first infrastructure BSS 601 of FIG. 7. A third stationSTA3 and a fourth station STA4 may constitute the second infrastructureBSS 602 of FIG. 7. Each of the stations STA1, STA2, STA3, and STA4 mayrefer to an AP or a terminal.

For example, the first station STA1 may be the same as the firstterminal 611 of FIG. 7, and the second station STA2 may be the same asthe first AP 610 of FIG. 7. The third station STA3 may be the same asthe second terminal 621 of FIG. 7, and the fourth station STA4 may bethe same as the second AP 620 of FIG. 7.

First, the first station STA1 may retrieve a channel during DIFS, andwhen a signal exceeding a preset signal size is not detected based onthe retrieval result (that is, when the channel is in an idle state),transmit an RTS frame 701 to the second station STA2 after contentionwindow (CW) according to a random back-off procedure. When normallyreceiving the RTS frame 701, the second station STA2 may transmit a CTSframe 702 as a response to the RTS frame 701. In this instance, thesecond station STA2 may transmit the CTS frame 702 after the SIFS from areception termination time of the RTS frame 701.

When normally receiving the CTS frame 702, the first station STA1 maytransmit a data frame 703 to the second station STA2 after the SIFS froma reception termination time of the CTS frame 702. When normallyreceiving the data frame 703, the second station STA2 may transmit anACK frame 704 as a response to the data frame 703 to the first stationSTA1. In this instance, the second station STA2 may transmit the ACKframe 704 after the SIFS from a reception termination time of the dataframe 703. When receiving the ACK frame 704, the first station STA1 maydetermine that the data frame 703 is normally received from the secondstation STA2.

Meanwhile, when receiving the RTS frame 701 from the first station STA1,the third station STA3 may set an NAV based on a period indicated by aduration field included in an MAC header of the RTS frame 701, and maynot transmit a corresponding frame for a period during which the set NAVis indicated. The fourth station STA4 cannot normally receive the RTSframe 701 or the CTS frame 702, and thereby does not set the NAV basedon the RTS frame 701 or the CTS frame 702. Thus, when there is data tobe transmitted to the third station STA3, the fourth station STA4 maytransmit an RTS frame 705 to the third station STA3 regardless of theNAV that is set based on the RTS frame 701 or the CTS frame 702. In thisinstance, the fourth station STA4 may retrieve a channel during DIFS,and when a signal exceeding a preset signal size is not detected basedon the retrieval result (that is, when the channel is in an idle state),transmit the RTS frame 705 to the third station STA3 after contentionwindow (for example, CW=2) according to the random back-off procedure.

The third station STA3 may receive the RTS frame 705 from the fourthstation STA4. However, the third station STA3 is in a state in which thethird station STA3 cannot transmit the corresponding frame by NAV thatis set based on the RTS frame 701 received from the first station STA1,and thereby cannot transmit a CTS frame 706 that is a response to theRTS frame 705 to the fourth station STA4. In this case, the fourthstation STA4 cannot receive the CTS frame 706 from the third stationSTA3 until a reception termination time (that is, CTS timeout) of theCTS frame 706 that is the response to the RTS frame 705, and thereforemay perform a re-transmission process of the RTS frame.

That is, the fourth station STA4 may retrieve a corresponding channelduring DIFS from the reception termination time of the CTS frame 706,and when a signal exceeding a preset signal size is not detected basedon the retrieval result (that is, when the channel is in to an idlestate), transmit an RTS frame 707 to the third station STA3 aftercontention window (for example, CW=4) according to the random back-offprocedure. In this instance, the RTS frame 705 fails to be transmitted,and therefore the contention window (CW) used for transmission of theRTS frame 707 may be twice the contention window (CW) used fortransmission of the RTS frame 705. Meanwhile, since the data frame 703transmitted from the first station STA1 and the RTS frame 707transmitted from the second AP 620 collide with each other, the thirdstation STA3 may not normally receive the RTS frame 707. In this case,the fourth station STA4 may not receive a CTS frame 708 from the thirdstation STA3 until the reception termination time of the CTS frame 708that is a response to the RTS frame 707, and thereby may perform there-transmission process of the RTS frame again.

In this manner, the fourth station STA4 may waste an unnecessary time bythe re-transmission of the RTS frame. That is, the performance of thecommunication system may be significantly degraded due to the blockednode problem.

The solutions to the exposed node problem and the blocked node problemwill be described in detail as below. A station that performs themethods according to the present invention may be the same as thestation shown in FIG. 1. In particular, a configuration of a processorconstituting the station shown in FIG. 1 may be as follows.

FIG. 9 is a block diagram illustrating a configuration of a processorconstituting a station.

Referring to FIG. 9, a processor 110 may include a channel connectionmanagement unit 111, an interference/non-interference station listmanagement unit 112, and a simultaneous transmission management unit113. Here, the channel connection management unit 111 may mean aconventional configuration that is responsible for transmission amongstations. The channel connection management unit 111 and theinterference/non-interference station list management unit 112 may beconnected to each other via a first interface 110-1 and a secondinterface 110-2. The channel connection management unit 111 and thesimultaneous transmission management unit 113 may be connected to eachother via a third interface 110-3 and a fourth interface 110-4. Theinterference/non-interference station list management unit 112 and thesimultaneous transmission management unit 113 may be connected to eachother via a fifth interface 110-5.

The interference/non-interference station list management unit 112 mayperform generation, management, updating, and the like of aninterference station list and a non-interference station list based oninformation transmitted from the channel connection management unit 111via the first interface 110-1. In addition, theinterference/non-interference station list management unit 112 maytransmit at least one of the interference station list and thenon-interference station list to the channel connection management unit111 via the second interface 110-2 in accordance with a request from thechannel connection management unit 111 via the first interface 110-1. Inaddition, the interference/non-interference station list management unit112 may transmit the at least one of the interference station list andthe non-interference station list to the simultaneous transmissionmanagement unit 113 via the fifth interface 110-5 in accordance with arequest from the simultaneous transmission management unit 113.

The simultaneous transmission management unit 113 may determine whethersimultaneous transmission is possible based on the at least one of theinterference station list and the non-interference station list acquiredfrom the interference/non-interference station list management unit 112,and perform simultaneous transmission with other communication objectswhen the simultaneous transmission is possible.

FIG. 10 is a flowchart illustrating a method for generatinginterference/non-interference station lists according to an embodimentof the present invention.

Referring to FIG. 10, in operation 5910, a first station may receive afirst frame from a second station through channel retrieval (forexample, CCA). Each of the first station and the second station mayrefer to an AP or a terminal. Here, the first frame may be a proberequest frame, an authentication request frame, an association requestframe, a reassociation request frame, an RTS frame, a data frame, or ablock acknowledgement request (BAR) frame.

In operation S920, the first station may acquire a receiver address (RA)of the first frame from an address field included in an MAC header ofthe first frame. In operation S930, the first station may determinewhether a station indicated by the receiver address of the first frameis the first station. In operation S940, when the station indicated bythe receiver address of the first frame is the first station, the firststation may transmit a response to the first frame to the second stationafter an SIFS from a reception termination time of the first frame.

On the other hand, when the station indicated by the receiver address ofthe first frame is a third station different from the first station, thefirst station may generate interference/non-interference station listsas follows. In operation S950, the first station may determine whetherto receive a second frame that is a response to the first frametransmitted from the third station indicated by the receiver address ofthe first frame within a preset time from the reception termination timeof the first frame. Here, the third station may refer to an AP or aterminal, and the preset time may refer to the SIFS. The second framemay be a probe response frame, an authentication response frame, anassociation response frame, a reassociation response frame, a CTS frame,an ACK frame, or a block acknowledgement (BA) frame.

In operation S960, when normally receiving the second frame within thepreset time, the first station may set the third station as aninterference station. In operation S970, the first station may generatean interference station list including identification information (forexample, MAC address, association identifier (AID), partial associationidentifier (PAID), and the like) of the third station and receptionpower information of the second frame measured in the first station.

On the other hand, in operation S980, when failing to normally receivingthe second frame within the preset time, the first station may set thethird station as a non-interference station. In operation S990, thefirst station may generate a non-interference station list includingidentification information of the third station and reception powerinformation of the second frame measured in the first station.

Hereinafter, a method for transmitting a frame based on the interferencestation list and the non-interference station list will be described indetail.

FIG. 11 is a flowchart illustrating a method for transmitting a frameaccording to an embodiment of the present invention.

Referring to FIG. 11, in operation S1010, a first station may receive afirst frame from a second station through channel retrieval (forexample, CCA). Each of the first station and the second station mayrefer to an AP or a terminal. Here, the first frame may be an RTS frame,a data frame, or a BAR frame.

In operation S1020, the first station may acquire a receiver address ofthe first frame from an address field included in an MAC header of thefirst frame. In operation S1030, the first station may determine whethera station indicated by the receiver address of the first frame is thefirst station. In operation S1040, when the station indicated by thereceiver address of the first frame is the first station, the firststation may transmit a response to the first frame to the second stationafter an SIFS from a reception termination time of the first frame.

On the other hand, when the station indicated by the receiver address ofthe first frame is a third station different from the first station, thefirst station may transmit a corresponding frame as follows. Inoperation S1050, the first station may determine whether the thirdstation (that is, the third station that transmits a second frame thatis a response to the first frame) indicated by the receiver address ofthe first frame is an interference station or a non-interference stationbased on an interference station list and a non-interference stationlist which are generated in advance. Here, the third station may referto an AP or a terminal. The second frame may be a CTS frame, an ACKframe, or a BA frame.

The interference station list and the non-interference station list maybe the same as the interference station list and the non-interferencestation list described with reference to FIG. 10. The interferencestation list may include identification information of an interferencestation and reception power information of a frame transmitted from theinterference station. The non-interference station list may includeidentification information of a non-interference station and receptionpower information of a frame transmitted from the non-interferencestation.

In operation S1060, when the identification information of the thirdstation is included in the interference station list (that is, when thethird station is the interference station), the first station mayreceive the second frame transmitted from the third station, set an NAVbased on a period indicated by a duration field included in an MACheader of the second frame, and may not transmit a frame during a periodindicated by the set NAV.

On the other hand, when the identification information of the thirdstation is included in the non-interference station list (that is, whenthe third station is the non-interference station), the first stationmay transmit a third frame to other communication objects. Specifically,in operation S1070, the first station may acquire, from thenon-interference station list, reception power information about theframe transmitted by the third station.

In operation S1080, the first station may retrieve a channel during apreset time based on the acquired reception power information. That is,the first station may adjust a preset signal size (that is, a signalsize used for determining an idle state of the channel) based on thereception power information acquired from the non-interference stationlist in order to remove an effect of the frame transmitted from thethird station when retrieving the channel. For example, the firststation may set a difference between the preset signal size andreception power indicated by the reception power information as a newpreset signal size, and determine whether a signal exceeding the newpreset signal size is detected through channel retrieval. Here, thepreset time may be a DIFS, a PIFS, or an AIFS.

In operation S1090, when the signal exceeding the new preset signal sizeis not detected during the preset time, the first station may determinethat the corresponding channel is in an idle state, and transmit thethird frame to other communication objects. Here, the third frame may bean RTS frame or a frame (hereinafter, referred to as a prevent to send(PTS) frame that is prevented from being transmitted to the firststation. The PTS frame may include at least one of a transmitter address(TA) of the PTS frame, period information during which transmission ofthe corresponding frame is stopped, and a receiver address of the PTSframe.

When having data to be transmitted to other communication objects, thefirst station may transmit the RTS frame as the third frame to the othercommunication objects. In this case, the first station may transmit adata frame to the other communication objects through exchange betweenthe RTS frame and the CTS frame. Through this, the exposed node problemmay be solved.

On the other hand, when not having data to be transmitted to the othercommunication objects, the first station may transmit the PTS frame asthe third frame. In this instance, the first station may transmit thePTS frame in a broadcast method, a multicast method, or a unicastmethod. Each of the communication objects having received the PTS framemay acquire a transmitter address of the PTS frame included in the PTSframe, and may not transmit a corresponding frame to the first stationindicated by the transmitter address. In addition, each of thecommunication objects having received the PTS frame may further acquireperiod information during which frame transmission is stopped, which isincluded in the PTS frame, and may not transmit the corresponding frameto the first station during a period indicated by the period informationduring which transmission of the frame is stopped. Through this, theblocked node problem may be solved.

FIG. 12 is a conceptual diagram illustrating an example of a method fortransmitting a data frame according to an embodiment of the presentinvention, and FIG. 13 is a conceptual diagram illustrating an exampleof a method for transmitting a PTS frame according to an embodiment ofthe present invention.

Referring to FIGS. 12 and 13, a first station STA1 and a second stationSTA2 may constitute the first infrastructure BSS 401 of FIG. 5 or thefirst infrastructure BSS 601 of FIG. 7. A third station STA3 and afourth station STA4 may constitute the second infrastructure BSS 402 ofFIG. 5 or the second infrastructure BSS 602 of FIG. 7. Each of thestations STA1, STA2, STA3, and STA4 may refer to an AP or a terminal.

For example, the first station STA1 may be the same as the firstterminal 411 of FIG. 5 or the first terminal 611 of FIG. 7, and thesecond station STA2 may be the same as the first AP 410 of FIG. 5 or thefirst AP 610 of FIG. 7. The third station STA3 may be the same as thesecond terminal 421 of FIG. 5 or the second terminal 621 of FIG. 7, andthe fourth station STA4 may be the same as the second AP 420 of FIG. 5or the second AP 620 of FIG. 7.

First, the first station STA1 may retrieve a channel during DIFS, andwhen a signal exceeding a preset signal size is not detected based onthe retrieval result (that is, when the channel is in an idle state),transmit an RTS frame 1101 to the second station STA2 after contentionwindow (CW) according to a random back-off procedure. When normallyreceiving the RTS frame 1101, the second station STA2 may transmit a CTSframe 1102 as a response to the RTS frame 1101. In this instance, thesecond station STA2 may transmit the CTS frame 1102 after the SIFS froma reception termination time of the RTS frame 1101.

When normally receiving the CTS frame 1102, the first station STA1 maytransmit a data frame 1103 to the second station STA2 after the SIFSfrom a reception termination time of the CTS frame 1102. When normallyreceiving the data frame 1103, the second station STA2 may transmit anACK frame 1104 as a response to the data frame 1103 to the first stationSTA1. In this instance, the second station STA2 may transmit the ACKframe 1104 after the SIFS from a reception termination time of the dataframe 1103. When receiving the ACK frame 1104, the first station STA1may determine that the data frame 1103 is normally received from thesecond station STA2.

Meanwhile, when receiving the RTS frame 1101, the third station STA3 mayacquire a receiver address of the RTS frame 1101 from an address fieldincluded in an MAC header of the RTS frame 1101. The third station STA3may determine whether the second station STA2 indicated by the receiveraddress is an interference station or a non-interference station basedon an interference station list and a non-interference station listwhich are generated in advance. Here, the interference station list andthe non-interference station list may be the same as the interferencestation list and the non-interference station list described withreference to FIG. 10. That is, the interference station list may includeidentification information of an interference station and receptionpower information of a frame transmitted from the interference station.The non-interference station list may include identification informationof a non-interference station and reception power information of a frametransmitted from the non-interference station.

When the identification information of the second station STA2 isincluded in the interference station list, the third station STA3 maydetermine the second station STA2 as the interference station. In thiscase, the third station STA3 may set an NAV based on the RTS frame 1101,and may not transmit the corresponding frame to other communicationobjects during a period indicated by the set NAV.

On the other hand, when the identification information of the secondstation STA2 is included in the non-interference station list, the thirdstation STA3 may determine the second station STA2 as thenon-interference station. The third station STA3 may retrieve a channelduring a preset time (SIFS) from the reception termination time of theRTS frame 1101, and determine presence/absence of a signal exceeding apreset size through channel retrieval. Here, the preset time (SIFS) maybe a DIFS, PIFS, or AIFS. In addition, the preset time (SIFS) may beless than an available channel idle period, and the available channelidle period may be a period from the reception termination time of theRTS frame 1101 to a reception start time of the data frame 1103.

Specifically, the third station STA3 may acquire, from thenon-interference station list, reception power information in the thirdstation STA3 with respect to a frame (for example, a CTS frame that is aresponse to the RTS frame) transmitted by the second station STA2. Thethird station STA3 may retrieve a corresponding channel during thepreset time (SIFS) based on the acquired reception power information.That is, the third station STA3 may adjust a preset signal size based onthe reception power information about the frame transmitted by thesecond station STA2 in order to remove the effect of the CTS frame 1102transmitted from the second station STA2 when retrieving the channel.For example, the third station STA3 may set a difference between thepreset signal size and reception power indicated by the reception powerinformation as a new preset signal size, and determine whether a signalexceeding the new preset signal size is detected through channelretrieval.

When the channel is in an idle state (that is, when the signal exceedingthe new preset signal size is not detected) during the preset time(SIFS), the third station STA3 may be operated as follows in accordancewith presence/absence of data to be transmitted to other communicationobjects.

Case in which Data to be Transmitted to Other Communication ObjectsExists

When having data to be transmitted to the fourth station STA4, the thirdstation STA3 may transmit an RTS frame 1105 to the fourth station STA4after the preset time (SIFS) from the reception termination time of theRTS frame 1101. In this instance, the third station STA3 may transmitthe RTS frame 1105 to the fourth station STA4 after contention window(CW) according to a random back-off procedure.

When normally receiving the RTS frame 1105, the fourth station STA4 maytransmit a CTS frame 1106 that is a response to the RTS frame 1105 tothe third station STA3. In this instance, the fourth station STA4 maytransmit the CTS frame 1106 after the SIFS from the receptiontermination time of the RTS frame 1105.

When normally receiving the CTS frame 1106, the third station STA3 maytransmit a data frame 1107 to the fourth station STA4 after the SIFSfrom the reception termination time of the CTS frame 1106. When normallyreceiving the data frame 1107, the fourth station STA 4 may transmit anACK frame 1108 as a response to the data frame 1107 to the third stationSTA3. In this instance, the fourth station STA4 may transmit the ACKframe 1108 after the SIFS from the reception termination time of thedata frame 1107. When receiving the ACK frame 1108, the third stationSTA3 may determine that the ACK frame 1108 is normally received in thefourth station STA4.

Here, transmission and reception of the RTS frame 1105, the CTS frame1106, the data frame 1107, and the ACK frame 1108 may be performed fromthe reception termination time of the RTS frame 1101 to the receptionstart time of the ACK frame 1104.

Case in which Data to be Transmitted to Other Communication Objects doesnot Exist

The third station STA3 may transmit a PTS frame 1109 after a preset time(SIFS) from the reception termination time of the RTS frame 1101. ThePTS frame 1109 may refer to a frame prevented from being transmitted tothe third station STA3. The PTS frame 1109 may include at least one of atransmitter address (that is, address of the third station STA3, periodinformation during which transmission of the frame is stopped, and areceiver address. The PTS frame 1109 may be transmitted in a broadcastmethod, a multicast method, or a unicast method.

Meanwhile, the fourth station STA4 may receive the PTS frame 1109 fromthe third station STA3. The fourth station STA4 may acquire atransmitter address from the PTS frame 1109, and may not transmit thecorresponding frame to the third station STA3 indicated by thetransmitter address. In addition, the fourth station STA4 may furtheracquire, from the PTS frame 1109, period information during whichtransmission of the frame is stopped, to and in this case, may nottransmit the corresponding frame to the third station STA3 indicated bythe transmitter address for the period during which transmission of theframe is stopped. The period information during which transmission ofthe frame is stopped may indicate a period from the receptiontermination time of the PTS frame 1109 to the reception start time ofthe ACK frame 1104.

FIG. 14 is a conceptual diagram illustrating another example of a methodfor transmitting a data frame according to an embodiment of the presentinvention, and FIG. 15 is a conceptual diagram illustrating anotherexample of a method for transmitting a PTS frame according to anembodiment of the present invention.

Referring to FIGS. 14 and 15, a first station STA1 and a second stationSTA2 may constitute the first infrastructure BSS 401 of FIG. 5 or thefirst infrastructure BSS 601 of FIG. 7. A third station STA3 and afourth station STA4 may constitute the second infrastructure BSS 402 ofFIG. 5 or the second infrastructure BSS 602 of FIG. 7. Each of thestations STA1, STA2, STA3, and STA4 may refer to an AP or a terminal.

For example, the first station STA1 may be the same as the firstterminal 411 of FIG. 5 or the first terminal 611 of FIG. 7, and thesecond station STA2 may be the same as the first AP 410 of FIG. 5 or thefirst AP 610 of FIG. 7. The third station STA3 may be the same as thesecond terminal 421 of FIG. 5 or the second terminal 621 of FIG. 7, andthe fourth station STA4 may be the same as the second AP 420 of FIG. 4or the second AP 620 of FIG. 7.

The first station STA1 may continuously transmit a data frame duringtransmission opportunity (TXOP). In addition, the first station STA1 maytransmit the data frame without exchange between the RTS frame and theCTS frame in the same manner as that in frame burst transmission orframe fragmentation transmission.

That is, the first terminal STA1 may retrieve a channel during DIFS, andwhen a signal exceeding a preset signal size is not detected based onthe retrieval result (that is, when the channel is in an idle state),transmit a data frame 1301 to the second station STA2 after contentionwindow (CW) according to a random back-off procedure. When normallyreceiving the data frame 1301, the second station STA2 may transmit anACK frame 1302 to the first station STA1 after an SIFS from a receptiontermination time of the data frame 1301. When receiving the ACK frame1302, the first station STA1 may determine that the data frame 1301 isnormally received in the second station STA2.

The first station STA1 may transmit a data frame 1303 to the secondstation STA2 after the SIFS from the reception termination time of theACK frame 1302. When normally receiving the data frame 1303, the secondstation STA2 may transmit an ACK frame 1304 to the first station STA1after the SIFS from the reception termination time of the data frame1303. When receiving the ACK frame 1304, the first station STA1 maydetermine that the data frame 1303 is normally received in the secondstation STA2.

Meanwhile, when receiving the data frame 1301, the third station STA3may acquire a receiver address of the data frame 1301 from an addressfield included in an MAC header of the data frame 1301. The thirdstation STA3 may determine whether the second station STA2 indicated bythe receiver address is an interference station or a non-interferencestation based on an interference station list and a non-interferencestation list which are generated in advance. Here, the interferencestation list and the non-interference station list may be the same asthe interference station list and the non-interference station listdescribed with reference to FIG. 10. That is, the interference stationlist may include identification information of an interference stationand reception power information of a frame transmitted from theinterference station. In addition, the non-interference station list mayinclude identification information of a non-interference station andreception power information of a frame transmitted from thenon-interference station.

When the identification information of the second station STA2 isincluded in the interference station list, the third station STA3 maydetermine the second station STA2 as the interference station. In thiscase, the third station STA3 may set an NAV based on the data frame1301, and may not transmit the corresponding frame to othercommunication objects during a period indicated by the set NAV.

On the other hand, when the identification information of the secondstation STA2 is included in the non-interference station list, the thirdstation STA3 may determine the second station STA2 as thenon-interference station. The third station STA3 may retrieve a channelduring a preset time (SIFS) from the reception termination time of thedata frame 1301, and determine presence/absence of a signal exceeding apreset size through channel retrieval. Here, the preset time (SIFS) maybe a DIFS, PIFS, or AIFS. In addition, the preset time (SIFS) may beless than an available channel idle period, and the available channelidle period may be a period from the reception termination time of thedata frame 1301 to a reception start time of the data frame 1303.

Specifically, the third station STA3 may acquire, from thenon-interference station list, reception power information in the thirdstation STA3 with respect to a frame (for example, an ACK frame that isa response to the data frame) transmitted by the second station STA2.The third station STA3 may retrieve a corresponding channel duringpreset time (SIFS) based on the acquired reception power information.That is, the third station STA3 may adjust a preset signal size based onthe reception power information acquired from the non-interferencestation list in order to remove the effect of the ACK frame 1302transmitted from the second station STA2 when retrieving the channel.For example, the third station STA3 may set a difference between thepreset signal size and reception power indicated by the reception powerinformation as a new preset signal size, and determine whether a signalexceeding the new preset signal size is detected through channelretrieval.

When the channel is in an idle state (that is, when the signal exceedingthe new preset signal size is not detected) during the preset time(SIFS), the third station STA3 may be operated as follows in accordancewith presence/absence of data to be transmitted to other communicationobjects.

Case in which Data to be Transmitted to Other Communication ObjectsExists

When having data to be transmitted to the fourth station STA4, the thirdstation STA3 may transmit an RTS frame 1305 to the fourth station STA4after the preset time (SIFS) from the reception termination time of thedata frame 1301. In this instance, the third station STA3 may transmitthe RTS frame 1305 to the fourth station STA4 after contention window(CW) according to a random back-off procedure.

When normally receiving the RTS frame 1305, the fourth station STA4 maytransmit a CTS frame 1306 that is a response to the RTS frame 1305 tothe third station STA3. In this instance, the fourth station STA4 maytransmit the CTS frame 1306 after the SIFS from the receptiontermination time of the RTS frame 1305.

When normally receiving the CTS frame 1306, the third station STA3 maytransmit a data frame 1307 to the fourth station STA4 after the SIFSfrom the reception termination time of the CTS frame 1306. When normallyreceiving the data frame 1307, the fourth station STA 4 may transmit anACK frame 1308 as a response to the data frame 1307 to the third stationSTA3. In this instance, the fourth station STA4 may transmit the ACKframe 1308 after the SIFS from the reception termination time of thedata frame 1307. When receiving the ACK frame 1308, the third stationSTA3 may determine that the data frame 1307 is normally received in thefourth station STA4.

Here, transmission and reception of the RTS frame 1305, the CTS frame1306, the data frame 1307, and the ACK frame 1308 may be performed fromthe reception termination time of the data frame 1301 to the receptionstart time of the ACK frame 1304.

Case in which Data to be Transmitted to Other Communication Objects doesnot Exist

The third station STA3 may transmit a PTS frame 1309 after a preset time(SIFS) from the reception termination time of the data frame 1301. ThePTS frame 1309 may refer to a frame prevented from being transmitted tothe third station STA3. The PTS frame 1309 may include at least one of atransmitter address (that is, address of the third station STA3), periodinformation during which transmission of the frame is stopped, and areceiver address. The PTS frame 1309 may be transmitted in a broadcastmethod, a multicast method, or a unicast method.

Meanwhile, the fourth station STA4 may receive the PTS frame 1309 fromthe third station STA3. The fourth station STA4 may acquire atransmitter address from the PTS frame 1309, and may not transmit thecorresponding frame to the third station STA3 indicated by thetransmitter address. In addition, the fourth station STA4 may furtheracquire, from the PTS frame 1309, period information during whichtransmission of the frame is stopped, and in this case, may not transmitthe corresponding frame to the third station STA3 indicated by thetransmitter address for the period during which transmission of theframe is stopped. The period information during which transmission ofthe frame is stopped may indicate a period from the receptiontermination time of the PTS frame 1309 to the reception start time ofthe ACK frame 1304.

FIG. 16 is a conceptual diagram illustrating still another example of amethod for transmitting a data frame according to an embodiment of thepresent invention, and FIG. 17 is a conceptual diagram illustratingstill another embodiment of a method for transmitting a PTS frameaccording to an embodiment of the present invention.

Referring to FIGS. 16 and 17, a first station STA1, a second stationSTA2, a third station STA3, and a fourth station STA4 may constitute afirst infrastructure BSS. A fifth station STA5 and a sixth station STA6may constitute a second infrastructure BSS. The first station STA1 maynormally receive frames transmitted from the second station STA2, thethird station STA3, the fourth station STA4, and the fifth station STA5,but may not normally receive a frame transmitted from the sixth stationSTA6.

The fifth station STA5 may normally receive the frames transmitted fromthe first station STA1, the second station STA2, the third station STA3,and the sixth station STA6, but may not receive the frame transmittedfrom the fourth station STA4. The sixth station STA6 may normallyreceive the frame transmitted from the fifth station STA5, but may notnormally receive the frames transmitted from the first station STA1, thesecond station STA2, the third station STA3, and the fourth stationSTA4.

That is, the first station STA1, the second station STA2, and the thirdstation STA3 may refer to an interference station with respect to thefifth station STA5. The fourth station STA4 may refer to anon-interference station with respect to the fifth station STA5. Here,each of the stations STA1, STA2, STA3, STA4, STA5, and STA6 may refer toan AP or a terminal.

First, the first station STA1 may retrieve a channel during DIFS, andwhen a signal exceeding a preset signal size is not detected based onthe retrieval result (that is, when the channel is in an idle state),transmit a data frame 1501 to the second station STA2, the third stationSTA3, and the fourth station STA4 in a multicast method after contentionwindow (CW) according to a random back-off procedure. Here, an ACKpolicy of the second station STA2 may be an implicit BA, and ACKpolicies of the third station STA3 and the fourth station STA4 may be anexplicit BA.

When receiving the data frame 1501, the second station STA2 may transmita BA frame 1502 that is a response to the received data frame 1501 tothe first station STA1. When receiving the BA frame 1502, the firststation STA1 may transmit a BAR frame 1503 to the third station STA3after an SIFS from a reception termination time of the BA frame 1502.When receiving the BAR frame 1503, the third station STA3 may transmit aBA frame 1504 that is a response to the data frame 1501 to the firststation STA1. When receiving the BA frame 1504, the first station STA1may transmit a BAR frame 1505 to the fourth station STA4 after the SIFSfrom the reception termination time of the BA frame 1504. When receivingthe BAR frame 1505, the fourth station STA4 may transmit a BA frame 1506that is a response to the data frame 1501 to the first station STA1.When receiving the BA frame 1506, the first station STA1 may transmit adata frame 1507 to the second station STA2, to the third station STA3,and the fourth station STA4 in the multicast method after the SIFS fromthe reception termination time of the BA frame 1506.

Meanwhile, the fifth station STA5 may receive the data frame 1501transmitted from the first station STA 1. The fifth station STA5 mayacquire a receiver address of the data frame 1501 from the data frame1501 and determine that the receiver address is the second station STA2,the third station STA3, and the fourth station STA4.

The fifth station STA5 may determine whether each of the second stationSTA2, the third station STA3, and the fourth station STA4 is aninterference station or a non-interference station based on aninterference station list and a non-interference station list which aregenerated in advance.

Here, the second station STA2 and the third station STA3 are assumed tobe the interference station, and the fourth station STA4 is assumed tobe the non-interference station.

The interference station list and the non-interference station list maybe the same as the interference station list and the non-interferencestation list described with reference to FIG. 10. That is, theinterference station list may include identification information of aninterference station and reception power information of a frametransmitted from the interference station. In addition, thenon-interference station list may include identification information ofa non-interference station and reception power information of a frametransmitted from the non-interference station.

When the identification information of the second station STA2 isincluded in the interference station list, the fifth station STA5 maydetermine the second station STA2 as the interference station. Thus, thefifth station STA5 may not attempt to transmit the corresponding framewhile the second station STA2 transmits the BA frame 1502.

When identification information of the third station STA3 is included inthe interference station list, the fifth station STA5 may determine thethird station STA3 as the interference station. Thus, the fifth stationSTA5 may not attempt to transmit the corresponding frame while the thirdstation STA3 transmits the BA frame 1504.

When identification information of the fourth station STA4 is includedin the non-interference station list, the fifth station STA5 maydetermine the fourth station STA4 as the non-interference station. Thefifth station STA5 may retrieve a channel during a preset time (SIFS)from the reception termination time of the BAR frame 1505, and determinepresence/absence of a signal exceeding a preset size through channelretrieval. Here, the preset time (SIFS) may be a DIFS, PIFS, or AIFS. Inaddition, the preset time (SIFS) may be less than an available channelidle period, and the available channel idle period may be a period fromthe reception termination time of the BAR frame 1505 to a receptionstart time of the data frame 1507.

Specifically, the fifth station STA5 may acquire, from thenon-interference station list, reception power information in the fifthstation STA5 with respect to a frame (for example, a BA frame that is aresponse to the data frame) transmitted by the fourth station STA4. Thefifth station STA5 may retrieve a corresponding channel during thepreset time (SIFS) based on the acquired reception power information.That is, the fifth station STA5 may adjust a preset signal size based onthe reception power information acquired from the non-interferencestation list in order to remove the effect of the BA frame 1506transmitted from the fourth station STA4 when retrieving the channel.For example, the fifth station STA5 may set a difference between thepreset signal size and reception power indicated by the reception powerinformation as a new preset signal size, and determine whether a signalexceeding the new preset signal size is detected through channelretrieval.

When the channel is in an idle state (that is, when the signal exceedingthe new preset signal size is not detected) during the preset time(SIFS), the fifth station STA5 may be operated as follows in accordancewith presence/absence of data to be transmitted to other communicationobjects.

Case in which Data to be Transmitted to Other Communication ObjectsExists

When having data to be transmitted to the sixth station STA6, the fifthstation STA5 may transmit an RTS frame 1508 to the sixth station STA6after the preset time (SIFS) from the reception termination time of theBAR frame 1505. In this instance, the fifth station STA5 may transmitthe RTS frame 1508 to the sixth station STA6 after contention window(CW) according to a random back-off procedure.

When normally receiving the RTS frame 1508, the sixth station STA6 maytransmit a CTS frame 1509 that is a response to the RTS frame 1508 tothe fifth station STA5. In this instance, the sixth station STA6 maytransmit the CTS frame 1509 after the SIFS from the receptiontermination time of the RTS frame 1508.

When normally receiving the CTS frame 1509, the fifth station STA5 maytransmit a data frame 1510 to the sixth station STA6 after the SIFS fromthe reception termination time of the CTS frame 1509. When normallyreceiving the data frame 1510, the sixth station STA 6 may transmit anACK frame 1511 as a response to the data frame 1510 to the fifth stationSTA5. In this instance, the sixth station STA6 may transmit the ACKframe 1511 after the SIFS from the reception termination time of thedata frame 1510.

Here, transmission and reception of the RTS frame 1508, the CTS frame1509, the data frame 1510, and the ACK frame 1511 may be performed fromthe reception termination time of the BAR frame 1505 to a receptionstart time of the response to the data frame 1507.

Case in which Data to be Transmitted to Other Communication Objects doesnot Exist

The fifth station STA5 may transmit a PTS frame 1512 after a preset time(SIFS) from the reception termination time of the BAR frame 1505. ThePTS frame 1512 may refer to a frame prevented from being transmitted tothe fifth station STA5. The PTS frame 1512 may include at least one of atransmitter address (that is, address of the fifth station STA5), periodinformation during which transmission of the frame is stopped, and areceiver address. The PTS frame 1512 may be transmitted in a broadcastmethod, a multicast method, or a unicast method.

Meanwhile, the sixth station STA6 may receive the PTS frame 1512 fromthe fifth station STA5. The sixth station STA6 may acquire a transmitteraddress from the PTS frame 1512, and may not transmit the correspondingframe to the fifth station STA5 indicated by the transmitter address. Inaddition, the sixth station STA6 may further acquire, from the PTS frame1512, period information during which transmission of the frame isstopped, and in this case, may not transmit the corresponding frame tothe fifth station STA5 indicated by the transmitter address for theperiod during which transmission of the frame is stopped. The periodinformation during which transmission of the frame is stopped mayindicate a period from the reception termination time of the PTS frame1512 to the reception start time of the response to the data frame 1507.

As described above, according to the present invention, the station inthe exposed node state may transmit the corresponding frame. Meanwhile,the station in the blocked node state may request transmission stop of aframe using the station itself as a destination, so that the frame usingthe station itself as the destination may be prevented from beingtransmitted. Thus, the performance of the WLAN system may be improved.

The embodiments of the present invention may be implemented in the formof program instructions that can be executed through various computermeans and recorded in a computer-readable medium. The computer-readablemedium may separately include program instructions, data files, datastructures, etc. or include a combination of them. The program commandsrecorded in the computer-readable medium may be specially designed andconfigured for the present invention, or known and available to those ofordinary skill in the field of computer software. The computer-readablemedium may mean a hardware device particularly configured to store andperform the program instructions such as a ROM, RAM, flash memory, orthe like. The hardware device may be configured to be operated as atleast one software module so as to perform the operations according tothe embodiments of the present invention, and vice versa.

Examples of the computer-readable medium include magnetic media, such asa hard disk, a floppy disk, and a magnetic tape, optical media, such asa CD-ROM and a DVD, magneto-optical media, such as a floptical disk, andhardware devices, such as a ROM, a RAM, and a flash memory, speciallyconfigured to store and perform program commands. Examples of theprogram instructions may include high-level language codes executable bya computer using an interpreter, etc. as well as machine language codesmade by compilers.

While the example embodiments of the present invention and theiradvantages have been described in detail, it should be understood thatvarious changes, substitutions, and alterations may be made hereinwithout departing from the scope of the invention.

What is claimed is:
 1. A method for generatinginterference/non-interference (I/NI) station lists which is performed ina first station (STA1) , the method comprising: receiving at the STA1 afirst frame (FRM1) from a second station (STA2), wherein the frame typeof the FRM1 comprises at least one of a probe request frame, anauthentication request frame, an association request frame, areassociation request frame, a request to send (RTS) frame, a dataframe, or a block acknowledgement request (BAR) frame; acquiring areceiver address (RA) of the FRM1 from the FRM1; setting a third station(STA3) as an interference station in the I/NI station lists when the RAof the FRM1 is addressed to the STA3 and when a second frame (FRM2) isreceived by the STA1 within a preset time (PT) set after receipt of theFRM1 such that the RA of the FRM2 from the STA3 is addressed to theSTA2, wherein the frame type of the FRM2 comprises at least one of aprobe response frame, an authentication response frame, an associationresponse frame, a reassociation response frame, a clear to send (CTS)frame, an acknowledgement (ACK) frame, or a block acknowledgement (BA)frame; setting the STA3 as a non-interference station in the I/NIstation lists when the RA of the FRM1 is addressed to the STA3 and whenthe FRM2 is received by the STA1 outside the PT set after receipt of theFRM1; and transmitting a prevent to send (PTS) frame when the STA1 is inan idle state such that the PTS frame comprises at least one of atransmitter address of the STA1, information about a period during whichtransmission to the STA1 is to be stopped, and the RA of the PTS framecorresponds to the STA3.
 2. The method of claim 1, further comprising:setting a network allocation vector (NAV) at the STA1 so that the STA1does not transmit a frame during a timed duration indicated by the setNAV when the STA3 is set as the interference station.
 3. The method ofclaim 2, wherein setting the NAV at the STA1 is based on the timedduration that corresponds to a duration field in a MAC header of theFRM2 from the STA3.
 4. The method of claim 1, wherein the I/NI stationlists comprises identification information of the STA3 and receptionpower information of the FRM2 measured by the STA1.
 5. The method ofclaim 1, wherein the FRM1 comprises the RTS frame from the STA2 and theFRM2 comprises the CTS frame from the STA3.
 6. The method of claim 1,wherein the PT is a short inter-frame space (SIFS).
 7. A method fortransmitting a frame which is performed by a first station (STA1), themethod comprising: receiving at the STA1 a first frame (FRM1) from asecond station (STA2), wherein the frame type of the FRM1 comprises atleast one of a probe request frame, an authentication request frame, anassociation request frame, a reassociation request frame, a request tosend (RTS) frame, a data frame, or a block acknowledgement request (BAR)frame; acquiring a receiver address (RA) of the FRM1 from the FRM1; anddetermining whether a third station (STA3) indicated by the RA of theFRM1 is an interference station or a non-interference station based oninterference/non-interference (I/NI) station lists generated in advance,wherein the interference station list of the I/NI station lists includesat least one station that transmits a response to the FRM1 within afirst preset time (PT1), and the non-interference station list of theI/NI station lists includes at least one station that transmits theresponse to the FRM1 outside the PT1; acquiring reception powerinformation about a second frame (FRM2) transmitted by the STA3 from theI/NI station lists, wherein the frame type of the FRM2 comprises atleast one of a probe response frame, an authentication response frame,an association response frame, a reassociation response frame, a clearto send (CTS) frame, an acknowledgement (ACK) frame, or a blockacknowledgement (BA) frame, retrieving a channel based on the receptionpower information during a second preset time (PT2), and transmitting athird frame (FRM3) after the PT2 when a signal exceeding a preset signalsize does not exist during the PT2 and after the PT2 from a time whenthe FRM1 has been received when the STA3 is determined as thenon-interference station, wherein the frame type of the FRM3 comprisesat least one of a probe request frame, an authentication request frame,an association request frame, a reassociation request frame, a RTSframe, a data frame, or a BAR frame.
 8. The method of claim 7, whereinthe FRM1 comprises at least one of the RTS frame, the data frame, or theBAR frame.
 9. The method of claim 7, further comprising: setting anetwork allocation vector (NAV) at the STA1 so that the STA1 does nottransmit a frame during a timed duration indicated by the set NAV whenthe STA3 is set as the interference station.
 10. The method of claim 7,wherein the the PT1 is short inter-frame space (SIFS).
 11. The method ofclaim 9, wherein setting the NAV at the STA1 is based on the timedduration that corresponds to a duration field in a MAC header of theFRM2 from the STA3.
 12. The method of claim 7, wherein the PT2 is shortinter-frame space (SIFS).
 13. The method of claim 7, wherein the PT2comprises at least one of a distributed coordination function (DCF)inter-frame space (DIFS), a point coordination function (PCF)inter-frame space (PIFS), or an arbitration inter-frame space (AIFS).14. The method of claim 7, wherein the FRM3 comprises a prevent to send(PTS) frame.
 15. The method of claim 14, wherein the PTS frame comprisesat least one of a transmitter address of the STA1, information about aperiod during which transmission to the STA1 is to be stopped, and theRA of the PTS frame corresponds to the STA3.
 16. A first station (STA1)comprising: a processor; and a memory in which at least one programcommand executed through the processor is stored, wherein the at leastone program command is executable to perform steps of: receiving at theSTA1 a first frame (FRM1) from a second station (STA2), wherein theframe type of the FRM1 comprises at least one of a probe request frame,an authentication request frame, an association request frame, areassociation request frame, a request to send (RTS) frame, a dataframe, or a block acknowledgement request (BAR) frame; acquiring areceiver address (RA) of the FRM1 from the FRM1; and determining whethera third station (STA3) indicated by the RA of the FRM1 is aninterference station or a non-interference station based oninterference/non-interference (I/NI) station lists generated in advance,wherein the interference station list of the I/NI station lists includesat least one station that transmits a response to the FRM1 within afirst preset time (PT1), and the non-interference station list of theI/NI station lists includes at least one station that transmits theresponse to the FRM1 outside the PT1; acquiring reception powerinformation about a second frame (FRM2) transmitted by the STA3 from theI/NI station lists, wherein the frame type of the FRM2 comprises atleast one of a probe response frame, an authentication response frame,an association response frame, a reassociation response frame, a clearto send (CTS) frame, an acknowledgement (ACK) frame, or a blockacknowledgement (BA) frame, retrieving a channel based on the receptionpower information during a second preset time (PT2), and transmittingthe a third frame (FRM3) after the PT2 when a signal exceeding a presetsignal size does not exist during the PT2 and after the PT2 from a timewhen the FRM1 has been received when the STA3 is determined as thenon-interference station, wherein the frame type of the FRM3 comprisesat least one of a probe request frame, an authentication request frame,an association request frame, a reassociation request frame, a RTSframe, a data frame, or a BAR frame.
 17. The STA1 of claim 16, whereinthe interference station list of the I/NI station lists includes atleast one station that transmits a response to the FRM1 within the PT1,and the non-interference station list of the I/NI station lists includesat least one station that fails to transmit the response to the FRM1within the PT1.
 18. The STA1 of claim 16, wherein the at least oneprogram command is executable to further perform a step of setting anetwork allocation vector (NAV) at the STA1 so that the STA1 does nottransmit a frame during a timed duration indicated by the set NAV whenthe STA3 is set as the interference station.
 19. The STA1 of claim 18,wherein setting the NAV at the STA1 is based on the timed duration thatcorresponds to a duration field in a MAC header of the FRM2 from theSTA3.
 20. The STA1 of claim 16, wherein the FRM3 comprises a prevent tosend (PTS) frame that requests stopping frame transmission to the STA1.